Sen. Marco Rubio has nabbed his first endorsement from a governor, announcing Monday that Kansas Gov. Sam Brownback is backing him for president.

"Marco Rubio is a true conservative who can unite the party and defeat Hillary Clinton or Bernie Sanders in the fall," Brownback said in a statement released by the Rubio campaign. "In the past, conservatives have been forced to make a choice between their head and their hearts. This year, we are fortunate to not have to make that choice."

"Marco Rubio has a proven track record of protecting life, defending religious liberty, and undoing Obamacare," Brownback's statement continued. "He will be a wonderful president, and I am proud to offer him my full support."

Brownback is the first governor to endorse Rubio, although the Florida Republican has collected endorsements from more Republican senators and representatives than any of his GOP presidential opponents. Rubio spokesman Jeremy Adler said the campaign is "honored" to have earned Brownback's endorsement.

"Just like Governor Brownback, Marco has consistently defended life, small government and free enterprise throughout his career in public service," Adler said in a statement. "We are honored to have earned the Governor's endorsement and are glad he is a part of our growing team of conservatives to ensure that Marco defeats the Democrats this November."

Only a handful of the country's Republican governors have endorsed a candidate for president. Neither Donald Trump, former Florida Gov. Jeb Bush nor Sen. Ted Cruz has gotten the backing of any governors, while Ohio Gov. John Kasich's sole gubernatorial endorsement is from Alabama Gov. Robert Bentley.